History Life APBioCh17


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History Life APBioCh17

  1. 1. History of Life on Earth
  2. 2. Spontaneous Generation <ul><li>Spontaneous generation is the proposal that living organisms can arise from nonliving matter </li></ul><ul><li>Medieval beliefs </li></ul><ul><ul><li>Microbes were thought to arise from broth </li></ul></ul><ul><ul><li>Maggots were thought to arise from meat </li></ul></ul><ul><ul><li>Mice were thought to arise from mixtures of sweaty shirts and wheat </li></ul></ul>
  3. 3. Spontaneous Generation Refuted <ul><li>The maggots-from-meat idea was disproved by Francesco Redi in 1668 </li></ul><ul><ul><li>He kept flies away from uncontaminated meat </li></ul></ul><ul><li>The broth-to-microorganism idea was disproved by Louis Pasteur and John Tyndall in the mid-1800s </li></ul>
  4. 4. Spontaneous Generation Refuted Broth in flask is boiled to kill preexisting microogranisms As broth cools, condensing water collects, sealing the mouth of the flask If neck is later broken off, outside air can carry microorganisms into broth
  5. 5. Spontaneous Generation Refuted <ul><li>Did spontaneous generation occur on early Earth? </li></ul><ul><li>Pasteur did not prove that spontaneous generation never happened </li></ul><ul><ul><li>He only showed that it does not happen under present-day conditions in an oxygen-rich atmosphere </li></ul></ul>
  6. 6. The First Living Things <ul><li>Alexander Oparin and John Haldane (1920s and 1930s) </li></ul><ul><ul><li>Noted that an oxygen-rich atmosphere would not have permitted the spontaneous formation of complex organic molecules </li></ul></ul><ul><ul><li>Speculated that the atmosphere of early Earth contained little oxygen </li></ul></ul><ul><ul><li>Proposed that prebiotic chemical evolution gave rise to life </li></ul></ul>
  7. 7. The First Living Things <ul><li>Oparin and Haldane envisioned that prebiotic chemical evolution occurred in four stages </li></ul><ul><ul><li>Prebiotic synthesis and accumulation of small organic molecules </li></ul></ul><ul><ul><li>Small organic molecules combined to form larger molecules </li></ul></ul><ul><ul><li>Origin of self-replicating molecules </li></ul></ul><ul><ul><li>Packaging of molecules within some kind of enclosing membrane </li></ul></ul>
  8. 8. Organic Molecules <ul><li>Stanley Miller and Harold Urey (1953) </li></ul><ul><ul><li>Noted that the atmosphere of early Earth probably contained methane, ammonia, hydrogen, and water vapor, but no oxygen </li></ul></ul>
  9. 9. Organic Molecules <ul><li>Miller and Urey (1953) </li></ul><ul><ul><li>Simulated early Earth’s atmosphere by mixing the above gases in a flask and adding an electrical discharge to simulate lightning </li></ul></ul><ul><ul><ul><li>Simple organic molecules appeared after a few days </li></ul></ul></ul>
  10. 10. The Experiment of Miller & Urey Electric spark simulates lightning storm Organic molecules appear after only a few days Condenser Cool water flow Electric spark chamber CH 4   NH 3   H 2 Boiling chamber Gases of primeval atmosphere Purified water H 2 O H 2 O
  11. 11. Organic Molecules <ul><li>Similar experiments by Miller and others have produced amino acids, short proteins, nucleotides, and ATP </li></ul><ul><li>Exact composition of “atmosphere” was unimportant </li></ul><ul><ul><li>Must contain carbon, hydrogen, and nitrogen, and exclude oxygen </li></ul></ul><ul><li>Type of energy source was unimportant </li></ul><ul><ul><li>Electrical discharge, UV light, and heat were equally effective </li></ul></ul>
  12. 12. Organic Molecules Accumulate <ul><li>The lack of both life and oxygen gas on early Earth allowed large quantities of organic molecules to accumulate in areas protected from UV radiation (beneath rock ledges, in oceans) </li></ul><ul><li>UV radiation bombarded early Earth’s surface because there was no ozone to block it </li></ul><ul><li>UV radiation can break apart organic molecules </li></ul><ul><li>Accumulated simple organic molecules combined to form complex organic molecules </li></ul>
  13. 13. RNA <ul><li>May have been the first self-reproducing molecule </li></ul><ul><li>Thomas Cech and Sidney Altman (1980s) discovered an RNA molecule ( ribozyme ) that could catalyze a chemical reaction, a role that was thought to be performed only by protein enzymes </li></ul>
  14. 14. RNA <ul><li>Since Cech and Altman’s initial discovery dozens of naturally-occurring ribozymes have been found that catalyze reactions including </li></ul><ul><ul><li>Cutting other RNA molecules </li></ul></ul><ul><ul><li>Splicing together different RNA fragments </li></ul></ul><ul><ul><li>Attaching amino acids to growing proteins </li></ul></ul>
  15. 15. RNA <ul><li>Since Cech and Altman’s initial discovery researchers have synthesized ribozymes that catalyze the replication of small RNA molecules </li></ul><ul><li>Discovery of ribozymes led to hypothesis that RNA preceded the origin of DNA </li></ul><ul><li>RNA served as </li></ul><ul><ul><li>The information-carrying genetic molecule </li></ul></ul><ul><ul><li>The enzyme catalyst for its own replication </li></ul></ul>
  16. 16. RNA <ul><li>Over time, DNA replaced RNA as the information-carrying genetic molecule and RNA took on its present role as an intermediary between DNA and protein </li></ul>
  17. 17. Membrane-Like Vesicles <ul><li>Vesicles are small, hollow spheres formed from proteins or proteins complexed with other compounds </li></ul><ul><ul><li>Have been formed artificially by agitating water-containing proteins and lipids </li></ul></ul>
  18. 18. Membrane-Like Vesicles <ul><li>Vesicles resemble living cells </li></ul><ul><ul><li>Have a well-defined outer boundary that separates internal and external environments </li></ul></ul><ul><ul><li>Depending on composition, membrane may be remarkably similar to that of a real cell </li></ul></ul><ul><ul><li>Under certain conditions, may absorb material from the external solution, grow, and divide </li></ul></ul>
  19. 19. Membrane-Like Vesicles <ul><li>Certain vesicles ( protocells ) may have been the precursors of living cells </li></ul>
  20. 20. Microspheres as Proto-Cells
  21. 21. When Did Life Arise on Earth? <ul><li>Earth formed about 4.5 billion years ago </li></ul><ul><li>Life arose 3.9 to 3.5 billion years ago during the Precambrian era </li></ul><ul><ul><li>Oldest fossil organisms found to date are estimated to be about 3.5 billion years old </li></ul></ul>
  22. 22. Earth's History Projected on a 24-hour Day Formation of Earth First Earth rocks 12 1 2 3 4 5 8 9 10 11 12 a.m. 6 7 1 2 3 4 5 7 8 9 10 11 MIDNIGHT NOON 6 p.m. First prokaryotes First atmospheric oxygen First eukaryotes First multicellular organisms First flowers First humans (11:59:40) First humans (11:59:40) Billions of years ago 4 3 2 1
  23. 23. Capturing the Sun’s Energy <ul><li>The first photosynthesizing organisms (ancestors of cyanobacteria) appeared about 3.5 billion years ago </li></ul><ul><li>Photosynthesis requires sunlight, CO 2 , and hydrogen </li></ul><ul><ul><li>Earliest source of hydrogen believed to be hydrogen sulfide </li></ul></ul><ul><ul><li>Eventually, water replaced hydrogen sulfide as the source of hydrogen and photosynthesis became water-based </li></ul></ul>
  24. 24. Increased Oxygen in Atmosphere <ul><li>Water-based photosynthesis resulted in the release of oxygen gas as a by-product </li></ul><ul><li>Initially, oxygen combined with iron in the Earth’s crust to form iron oxide </li></ul><ul><li>Subsequently, oxygen began accumulating in the atmosphere </li></ul><ul><ul><li>Chemical analysis of rocks suggests that significant levels of atmospheric oxygen first appeared about 2.2 billion years ago </li></ul></ul>
  25. 25. Aerobic Metabolism <ul><li>The accumulation of oxygen in Earth’s atmosphere probably </li></ul><ul><ul><li>Exterminated many anaerobic organisms </li></ul></ul><ul><ul><li>Provided the environmental pressure for the evolution of aerobic metabolism </li></ul></ul><ul><li>The evolution of aerobic metabolism was significant because aerobic organisms can harvest more energy per food molecule than anaerobic organisms </li></ul>
  26. 26. Membrane-Enclosed Organelles <ul><li>The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago </li></ul><ul><li>Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis ) </li></ul>
  27. 27. Probable Origin of Mitochondria & Chloroplasts Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium Aerobic bacterium Descendents of engulfed bacterium evolve into mitochondria Photosynthetic bacterium Mitochondria-containing cell engulfs photosynthetic bacteria Descendents of photosynthetic bacteria evolve into chloroplasts
  28. 28. Evolution of Mitochondria <ul><li>Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest </li></ul><ul><li>Predatory cell and bacterium gradually enter into a symbiotic relationship </li></ul><ul><li>Descendants of engulfed bacterium evolve into mitochondria </li></ul>
  29. 29. Evolution of Chloroplasts <ul><li>Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium </li></ul><ul><li>Predatory cell and bacterium gradually enter into a symbiotic relationship </li></ul><ul><li>Descendants of engulfed bacterium evolve into chloroplasts </li></ul>
  30. 30. Evidence for Endosymbionts <ul><li>Many biochemical features are shared by eukaryotic organelles and living bacteria </li></ul><ul><li>Mitochondria, chloroplasts, and centrioles contain their own supply of DNA </li></ul><ul><li>Living intermediates (modern cells that host bacterial endosymbionts) </li></ul><ul><ul><li>Pelomyxa palustris harbors aerobic bacteria </li></ul></ul><ul><ul><li>Paramecium harbors photosynthetic bacteria </li></ul></ul>
  31. 31. Modern Intracellular Symbiosis Paramecium sp. Chlorella sp, a green alga
  32. 32. Cell Size <ul><li>Once predation evolved, increased cell size became an advantage </li></ul><ul><ul><li>Larger cells could more easily engulf smaller cells and they could move faster </li></ul></ul><ul><li>However, organisms larger than a millimeter in diameter can survive only in one of two ways </li></ul><ul><ul><li>Have a low metabolic rate </li></ul></ul><ul><ul><li>Be multicellular </li></ul></ul>
  33. 33. Some Algae Become Multicellular <ul><li>The first multicellular organisms appeared in the seas about 1 billion years ago </li></ul><ul><li>For plants, multicellularity allowed: </li></ul><ul><ul><li>Some protection from predation </li></ul></ul><ul><ul><li>Specialization of cells (plants were able to anchor themselves in the brightly lit waters of the shoreline) </li></ul></ul>
  34. 34. Some Algae Become Multicellular <ul><li>For animals, multicellularity allowed </li></ul><ul><ul><li>More efficient predation </li></ul></ul><ul><ul><li>More effective escape from predators </li></ul></ul>
  35. 35. Animal Diversity <ul><li>Fossil traces of animal tracks and burrows have been found in 1 billion-year-old rocks </li></ul><ul><li>Fossils of invertebrate animals (animals lacking backbones) have been collected from rocks 610 million to 544 million years old </li></ul><ul><li>The oldest rock layers included fossils of ancestral sponges and jellyfish </li></ul><ul><li>Subsequent rock layers revealed fossils of ancestral worms, mollusks, and arthropods </li></ul>
  36. 36. The Cambrian Explosion <ul><li>Most of the major phyla of animals had made their appearance by the Cambrian period of the Paleozoic era (544 million years ago) </li></ul><ul><li>The Cambrian period was marked by an “explosion” in animal diversity (may have resulted from coevolution of predator and prey) </li></ul><ul><li>Great diversity of ocean life arose during the Silurian period… </li></ul>
  37. 38. The Appearance of Fishes <ul><li>Fishes appeared in the fossil record about 530 million years ago </li></ul><ul><li>They were the first vertebrates (animals with backbones) </li></ul><ul><li>Over time, fish became the dominant predators in the oceans </li></ul><ul><ul><li>Faster than invertebrates </li></ul></ul><ul><ul><li>Possessed more acute senses and larger brains than invertebrates </li></ul></ul>
  38. 39. The Transition to Land <ul><li>The evolution of land plants </li></ul><ul><ul><li>The first land plants </li></ul></ul><ul><ul><ul><li>Mosses and ferns </li></ul></ul></ul><ul><ul><ul><li>Continued water dependency </li></ul></ul></ul><ul><ul><li>Conifers - the invasion of dry habitats </li></ul></ul><ul><ul><li>Flowering plants </li></ul></ul><ul><ul><ul><li>The dominant plant form today </li></ul></ul></ul><ul><ul><ul><li>Pollination by insects </li></ul></ul></ul>
  39. 40. Evolution of Terrestrial Animals <ul><li>Arthropods </li></ul><ul><li>Lobefin fish to amphibians </li></ul><ul><li>Amphibians to reptiles </li></ul><ul><ul><li>The age of the dinosaurs </li></ul></ul><ul><ul><li>Reptiles and maintenance of body temperature </li></ul></ul><ul><li>Birds </li></ul><ul><ul><li>Insulating feathers retain body heat </li></ul></ul><ul><ul><li>Evolution of feathers for flight </li></ul></ul><ul><li>Mammals </li></ul><ul><ul><li>Insulating hair retains body heat </li></ul></ul><ul><ul><li>Live births and mammary glands </li></ul></ul>
  40. 41. Multicellular Organisms <ul><li>Advantages of multicellularity </li></ul><ul><li>Challenges of multicellularity </li></ul><ul><li>The first multicellular organisms </li></ul><ul><ul><li>Plants - primitive marine algae </li></ul></ul><ul><ul><li>Animals - marine invertebrates </li></ul></ul><ul><li>The transition to land </li></ul>
  41. 42. Diversity over Time 200 0 400 600 800 Millions of Years Ago Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Tertiary Number of Families Mass Extinctions 500 400 300 200 100 0 600
  42. 43. Plate Tectonics & Climate Change
  43. 44. Human Evolution <ul><li>Primate evolution </li></ul><ul><ul><li>Grasping hands - precision grip and power grip </li></ul></ul><ul><ul><li>Binocular and color vision with overlapping fields of view </li></ul></ul><ul><ul><li>Large brain - allows fairly complex social systems </li></ul></ul>
  44. 45. Hominid Evolution I <ul><li>The evolution of Dryopithecines - between 20 and 30 million years ago </li></ul><ul><li>Australopithecines - the first true hominids </li></ul><ul><ul><li>Appeared 4 million years ago (fossils) </li></ul></ul><ul><ul><li>Walked upright </li></ul></ul><ul><ul><li>Large brains </li></ul></ul><ul><li>Homo habilis - 2 million years ago </li></ul><ul><ul><li>Larger body and brain </li></ul></ul><ul><ul><li>Ability to make crude stone and bone tools </li></ul></ul>
  45. 46. Hominid Evolution II <ul><li>Homo erectus - 1.8 million years ago </li></ul><ul><ul><li>Face of modern human </li></ul></ul><ul><ul><li>More socially advanced </li></ul></ul><ul><ul><li>Used fire & sophisticated stone tools </li></ul></ul><ul><li>Homo sapiens - 200,000 years ago </li></ul><ul><li>Neanderthals evolved 100,000 years ago </li></ul><ul><ul><li>Similar to humans - muscular, fully erect, dexterous, large brains </li></ul></ul><ul><ul><li>Developed ritualistic burial ceremonies </li></ul></ul><ul><li>Cro-Magnons evolved 90,000 years ago </li></ul><ul><ul><li>Direct descendants of modern humans </li></ul></ul><ul><ul><li>Were artistic and made precision tools </li></ul></ul>
  46. 47. Possible Human Line of Descent Millions of Years Ago Ardipithecus ramidus A. boisei A. africanus Australopithecus afarensis A. robustus Homo habilis H. erectus H. heidel- bergensis H. neander- thalensis Homo ergaster H. sapiens 5 4 3 2 1 0
  47. 48. The “Out of Africa” Theory H. erectus spread began ~1.8 mya H. sapiens spread began ~100 kya
  48. 49.   The “Multiregional”  Hypothesis     Regional pops of H. erectus may have evolved into H. sapiens while intermingling.
  49. 50. The End